1. Field of the Invention
The present invention relates to an organic micro-cavity laser, and more particularly to an organic micro-cavity laser comprising an active layer made of an organic material.
2. Prior Art of the Invention
An organic laser diode having an active layer composed of an organic material is generally superior to the conventional semiconductor laser diode because the organic laser diode does not have disadvantage such as a lattice mismatching during the epitaxial growth of the semiconductor laser diode. Also, the organic laser diode can be manufactured by a simple process. Furthermore, since the organic laser diode can accomplish the lasing of all the visible lights according to the synthetic process of the organic material as an active layer, the intensive researches for the organic laser diode have been accomplished to utilize as the next generation visible laser diode.
FIG. 1 is a cross-sectional view for showing the conventional optical pumping organic micro-cavity laser.
Referring to FIG. 1, the conventional organic micro-cavity laser comprises a bottom mirror layer 102 formed on a substrate 101, an active layer 103 formed on the bottom mirror layer 104 and a top mirror layer 104 formed on the active layer 103. In the conventional organic micro-cavity laser, those layers 102, 103, 104 are vertically piled up so as to accomplish the lasing characteristic by the optical pumping.
The heat is generated in the organic material during the operation of the laser since the electrical conductivity of the organic material is lower than that of the semiconductor. The lasing characteristic of the organic laser may fatally deteriorate by the generated heat. Thus, the configuration as shown in FIG. 1 cannot be applied to an electrical pumped laser diodes which implements the lasing by not the optical pumping but the electrical pumping. However, it has not been developed that the mirror layer composed of an organic material having good electrical conductivity which is suitable for the organic micro-cavity laser. Therefore, the electrical pumping micro-cavity laser has the configuration as shown in FIG. 2. That is, the electrical pumping micro-cavity laser comprises a bottom mirror layer 202 formed on a substrate 201, a transparent bottom electrode 203 formed on the bottom mirror laser 202, an active layer 204 made of an organic material and formed on the bottom electrode 203 and a top electrode 205 formed on the active layer 205. The conventional electrical pumping micro-cavity laser, however, cannot sufficiently reduce the optical loss because the conventional electrical pumping laser does not have a top mirror layer. Also, the conventional electrical pumping micro-cavity laser cannot have good lasing characteristic since the cavity does not have good electrical property.
Considering the above-mentioned problems, it is an object of the present invention to provide an organic micro-cavity having a top mirror layer and an active layer which can efficiently implement current injecting to the active layer so as to minimize the optical loss in a cavity.
To achieve the object of the present invention, there is provided an organic micro-cavity laser comprising a bottom mirror layer formed on a substrate, a bottom electrode formed on the bottom mirror layer, an active layer formed on the bottom electrode, a top electrode having a ring shape formed on a peripheral portion of the active layer and a top mirror layer formed on the active layer except the peripheral portion of the active layer.
Preferably, the bottom and the top mirror layers respectively have multi layer structures composed of distributed Bragg reflectors and the bottom and the top mirror layers are composed of an organic material such as SiOx/TiOx or SiOx/MgOx.
The bottom and the top mirror layers have thickness of xcex/4n wherein xcex means a wavelength and n represents a reflective index.
An uppermost layer of the bottom mirror layer and the bottom electrode have thicknesses of xcex4n, respectively, or thickness of the uppermost layer of the bottom mirror layer and the bottom electrode have a xcex/4n thickness.
The bottom electrode is composed of an indium tin oxide.
The active layer is preferably made of an organic material consisted of a single molecule or a polymer.
According to one preferred embodiment of the present invention, the active layer is a luminescent layer of single layer.
As for another preferred embodiment of the present invention, the active layer comprises a hole transport layer, a luminescent layer formed on the hole transport layer and an electron transport layer formed on the luminescent layer. As for another preferred embodiment of the present invention, the active layer can comprise a first barrier layer formed on the hole transport layer, a luminescent layer formed on the first barrier layer, and a second barrier layer formed on the luminescent layer. At that time, the active layer has a single well structure and the first and the second barrier layers are composed of materials having band gaps larger than a band gap of the luminescent layer.
According to still another embodiment of the present invention, the active layer comprises a hole transport layer, a plurality of barrier layers formed on the hole transport layer, a plurality of luminescent layers respectively formed between the barrier layers and an electron transport layer formed on an uppermost layer of the barrier layers. In this case, the active. layer has a multi well structure.
Preferably, the top electrode is composed of one metal selected from the group consisting of aluminum, calcium, lithium, magnesium and an alloy of those metals and the top electrode has a ring shape.
Therefore, the organic micro-cavity laser of the present invention can greatly reduce the optical loss in the cavity since the laser has the bottom mirror layer, the active layer and the top mirror layer. In addition, the injection of current can be sufficiently accomplished because the top electrode having the ring shape is formed at the peripheral portion of the active layer so as to inject the current to the active layer. Also the organic micro-cavity laser can be lased by the electrical pumping.